1. Field
This disclosure relates generally to high frequency millimeter wave integrated circuit amplifiers, and more particularly to a multiple stage amplifier tuned to a specific operating frequency and having a serpentine signal path.
2. Description of the Related Art
The design and manufacture of high frequency, millimeter wave integrated circuit devices presents many challenges not found in the construction of other types of integrated circuits. However, the design and manufacture of circuits for operation in the W-band and above, frequencies of approximately 75 GHz and above, present particular challenges, as circuits and structures suitable for use even at lower millimeter wave frequencies, for example as may be suitable for devices operating at 30 GHz, do not function similarly or adequately at 75 GHz and above.
The placement and configuration of signal and voltage lines can present substantial problems of resonance or “ringing” of the circuits. These problems are heightened when the integrated circuit is an amplifier, particularly one having multiple stages and offering relatively high gain and power. In a high gain multiple stage amplifier, even a slight amount of feedback may cause self-oscillation. Such feedback may occur due to coupling through power lines and/or coupling between signal lines. An amplifier designed to occupy a minimal area on a substrate, for example a minimally-sized semiconductor die, may be particularly prone to oscillation due to feedback. However, forming such an amplifier on a minimally-sized die is highly advantageous from a cost perspective, as smaller die will yield more die per semiconductor wafer, thus providing more devices for essentially no increase in the cost of wafer processing. Additionally and importantly, from an application perspective, the smaller a die may be made, the less space it takes in a final system; and such smaller size is often a significant factor in the system design.
Conventional, relatively high power, multi-stage, millimeter wave amplifier integrated circuits are designed with relatively large spaces between signal lines and other components in order to avoid the above-described ringing and feedback. While these design rules are generally effective for such purposes, the resulting large spaces increase the total area occupied on a die by such an amplifier.
Additionally, with such conventional design methodologies, a substantial portion of the integrated circuit area may be devoted to distributing gate and drain bias voltages to the amplifier stages. One conventional approach to power distribution is to route one or more power buses along the periphery of the chip. A plurality of bypass capacitors may be provided form the power bus to ground to minimize noise on the power bus from the high-frequency signals being amplified. Individual leads may then connect from the power bus to each amplifier stage. A second conventional method for bias voltage distribution is to provide separate bias pads for each amplifier stage, which allows the use of external components to prevent noise or feedback from coupling between stages via the bias voltage distribution network. With either approach, the bias voltage distribution network may occupy a substantial area on the die. Accordingly, for such high frequency millimeter wave amplifiers, the conventional design criteria and methods tend to increase the size of the device where compactness would be an asset.